Mobile communication devices, including cellular phones, personal digital assistants (PDAs), smart phones, other types of mobile phones, and the like, (herein also collectively referred to as mobile phones or smart phones) are being used not just for communication (voice and text), but also to take photos, send text messages, listen to music, surf the internet, do word processing, watch movies, and the like. Consumers are also becoming interested in using their mobile communication devices to perform various transactions (e.g., transfer funds, purchase products, etc.) traditionally provided by RFID tags, contact credit cards, and contactless credit cards.
Radio-frequency identification (RFID) is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, attached to an object, to an RFID reader for the purpose of identifying and performing some operation, e.g., tracking the object, payment of a transit fare, or performing some other transaction. Some RFID tags can be read from several meters away and beyond the line of sight of the reader. However, most such tags are short range, because they function using passive inductive coupling in the near-field, i.e., their range of operation is on the order of a few centimeters to a few tens of centimeters. The tag's information is stored electronically and typically includes an ID number and other stored data.
RFID tags typically contain at least two parts: an integrated circuit for storing and processing information, for modulating and demodulating a radio frequency (RF) signal, and for other specialized functions; and an antenna for receiving and transmitting the signal. An RFID reader transmits an encoded radio signal to interrogate the tag. The tag receives the message and responds with its identification information. The RFID reader typically is designed to enable it to discriminate between several tags that might be within the range of the RFID reader, enabling the almost parallel reading of tags.
Contactless smart cards are related to RFID tags but typically will also include writeable memory or microcontroller processing capability. Contactless smart cards are sometimes called contactless credit cards and include a Secure Element (SE) that enables communications between the card and the reader, e.g., a point of sale (POS) terminal, to be encrypted. Contactless smart cards are often used when transactions must be processed quickly or hands-free, such as on mass transit systems, where a smart card can be used to pay a transit fare without even removing it from a wallet. The standard protocol for contactless smart card communications is ISO 14443.
There are a variety of different RFID and contactless card standards and most operate in the 13.56 MHz Industrial Scientific and Medical (ISM) band residing within the High Frequency (HF) band. These include the ISO 14443 standard for contactless credit cards, e.g., Sony's Felica, NXP's Mifare, NXP's DESFire, all of which are commonly used for contactless transit fare payment; and the ISO 15693 standard for vicinity contactless smart cards, commonly used for access control. Pursuant to these various standards, the reader, RFID tag, and contactless smart card each have their own loop antenna, and employ inductive coupling at close range as the air interface to communicate with each other. The loop antenna of the reader and the loop antenna of the RFID tag (or to the contactless smart card) inductively couple to each other. This inductive mutual coupling is analogous to a weakly coupled transformer, where the degree of coupling varies with the position and orientation of the RFID tag or contactless smart card relative to the reader antenna. The field generated by the reader becomes weaker at more distant positions and for orientations of the RFID tag or contactless card that decrease the cross-sectional antenna area of the RFID tag or contactless card in the flux lines of the field generated by the reader. The reader actively generates a field and modulates it to transmit data to the RFID tag or contactless card. To receive the RFID tag or contactless card response, the reader ceases its own modulation, but continues to actively generate a field. The RFID tag inductively couples to the field generated by the reader, and operates by parasitically drawing power from the field. The RFID tag or contactless card applies passive load modulation to the reader-generated field to send data to the reader. The RFID tag or contactless card performs load modulation by varying the termination impedance applied to its own resonant antenna. This varying impedance is inductively coupled to the reader, modulating the load presented to the reader output, in turn modulating the field intensity and the voltage at the reader's receive port. Since the RFID tag or contactless smart card performs passive load modulation, rather than actively generating a field of its own, it does not require much power to operate, which makes it viable to operate parasitically off the reader's field.
Active RFID tags that have a battery or other self-contained source of power also exist, although they are less common. Active RFID tags are often used when an extended range of communication is desired.
Another category of near field device is also known in the art for operation in the HF band. This device is called a Near Field Communication (NFC) device and it operates at 13.56 MHz pursuant to its own set of protocols, e.g., ISO 18093 and ECMA 340. NFC devices enable simplified transactions, data exchange, and wireless connections between two devices in close proximity to each other. The essence of NFC is short-range wireless communication that is both safe and effective.
The maximum distance for near field devices is typically about 20 cms, which minimizes the possibility that an unauthorized communication will take place. The maximum distance for contactless smart cards is typically about 3 to 6 centimeters, and about 2 to 3 centimeters for NFC devices.
Many smart phones known in the art now contain embedded NFC devices to add 13.56 MHz proximity contactless functions, including card emulation, peer to peer, reader/writer, to mobile phones and other consumer electronic devices. This enables users of NFC enabled mobile phone to perform a range of additional capabilities not previously associated with mobile phones. These capabilities include: emulating a plastic contactless credit card to make NFC payments in a manner compatible with existing contactless point-of-sale readers; collecting and redeeming electronic coupons; accessing buildings and other secure areas having proximity reader controlled door locks; exchanging electronic business cards between devices; and tapping a smart poster to get additional production information from a web site. Nokia, for example, currently has a mobile phone with an embedded RFID tag that enables the phone to be used as a credit card and for accessing bank accounts.
Specialized microSD cards are also now available and, when inserted into a mobile phone, enable the phone to act as both a passive tag and an RFID reader. Using the microSD, a user's phone can be linked to bank accounts and used for mobile payments.
FIG. 1 is an example of a prior art mobile phone that includes an embedded NFC system for enabling the mobile phone to perform both contactless payments and two-way NFC communications. As seen in FIG. 1, NFC device in mobile phone 700 includes a controller 731 for controlling the operation of an NFC transceiver IC 720 via an interface 705, such as a parallel general purpose I/O bus. Also connected to transceiver 720 is a secure element 713 via a second interface 707, such as a single wire protocol (SWP) interface. This protocol is typically used for communication between a secure element (SE) and an NFC transceiver. Transceiver 720 is connected to an antenna 701 via a conventional matching network 725 to enable the NFC system to communicate with an external transceiver 743 having an antenna 741 (shown in phantom).
The drawback of this system is that the SE is not directly attached to its own dedicated antenna, for receipt of contactless data, and load modulation of the antenna to send contactless data. There is only one antenna in the system, the antenna 701 connected to NFC transceiver 720 via matching network 725. The SE performs digital communication with the NFC transceiver 720 via SWP, and the transceiver 720 performs the analog load modulation of its antenna, on behalf of the SE. The NFC transceiver 720 matching network 725 is not optimal for passive load modulation on behalf of the SE, so there is a compromise in performance.
A limitation of the prior art is that these embedded systems or external cards being used with mobile phones use a single antenna for both the RFID/NFC transceiver and the secure element. These prior art devices are therefore required to compromise the design of their single antenna and circuit networks for the divergent requirements of different near field devices.
More specifically, the design and tuning of a single antenna and the design and topology of a single matching network cannot be simultaneously optimized for the divergent requirements of different modes of operation, e.g., where one near field device is generating an active field using the antenna, and where a second near field device operates to vary the termination impedance applied to the antenna to create passive load modulation of the reader's generated field. The result is compromised range and performance for both modes of operation.
For example, an optimal matching network topology for a specific RFID transceiver may include two stages, the first stage comprising a balanced series inductor, shunt capacitor low pass filter stage, and the second stage comprising another balanced series/shunt capacitor stage for additional matching. The low pass filter stage is necessary to attenuate spurious emissions produced during active field generation, to comply with regulatory requirements that limit the allowable level of unintentional radiated emissions. The antenna used with active field generation requires wider printed circuit board traces, to support high current during active field generation.
The optimal matching network for a contactless SE, whose ISO 14443 interface employs passive load modulation, is completely different. The optimal circuit topology between the SE and the antenna is a single resonating capacitor. As the SE does not actively transmit any field, no filter stage is necessary to comply with regulatory requirements. For this mode of operation, an antenna with narrower traces is sufficient, as the contactless SE does not generate an active field, so the currents are lower.